tiny bodies breaking physics engine

[jbm222]

The attached lvledit.love is a wysiwyg level editor in its infant stages. Use the arrow keys to move the ball around. Left-click and drag to draw rectangles. Use the scroll wheel to switch between "fixed" (i.e. object that don't move) and "mobile" objects.

So here's the problem... when I draw really tiny objects, it crashes. The easiest way to reproduce the problem is to just click once. The attached error.jpg shows the error message that I get. This is for love 0.6.2, and I'm running on Windows Vista at the moment.

I know the code is kind of ugly at the moment as I'm still just getting the hang of lua. I'm not used working with a language that doesn't have OOP built into it. Anyway, any help figuring out why tiny objects break my "game" would be appreciated.

[bartbes]

Box2D loves to kill love, so yeah it's Box2D's fault. Anyway, what it means is that the distance between two points on the X-axis less than 0.0, which it can't handle.

[kikito]

Making objects of 0 size doesn't make sense on the context of Box2D. The crashes make sense if you are trying to create not just tiny, but "cero-length" objects - it's its way of telling you that what you are asking it to do isn't possible.

I suggest you add a minimum dimension for your objects (1x1?), so if the height/width received is smaller, than it, it is reset to the minimum. The user clicking would generate very tiny objects - just no 0 length.

Alternatively, you can check the dimensions before creating and just cancel the creation if width or height are too small. The user clicking would not generate objects at all on that case.

[bartbes]

Don't forget LÖVE scales.

[The Burrito]

The smallest "safe" object is .1 X .1 units, and that should be your cutoff point, by default LÖVE scale is 30px/unit, thus 3X3 pixels is the default minimum.

I have a similar box drawing tool for my editor, and it simply cancels creation of the object if its less than 2X2 (I have a smaller physics scale).

Technically nothing is crashing, Box2D is simply informing us that it didn't create the shape. It would be nice if there was a way to suppress these messages, or even better if the functions to create shapes returned a success / fail .

[bartbes]

File a report.

[jbm222]

The smallest "safe" object is .1 X .1 units, and that should be your cutoff point, by default LÖVE scale is 30px/unit, thus 3X3 pixels is the default minimum.

My code was based on a tutorial which set the scale to 64px/unit. I added a check that would force the smallest objects to 4x4, but I guess it needed to be 6x6 to work with the scale. Thanks!

Should there be a bug/issue opened about this? I was surprised to see the assertion failure reported by the C++ runtime. If there's no return value from Box2D, then LÖVE could do the bounds checking before calling into the library.

[Robin]

Should there be a bug/issue opened about this? I was surprised to see the assertion failure reported by the C++ runtime. If there's no return value from Box2D, then LÖVE could do the bounds checking before calling into the library.

I agree: we simple lovers should not be exposed to the dark magic of Box2D (at least not that easily).